True or false: medical studies often use a relatively large sample (in this case, 3980) because disease occurrences can be rare and difficult to observe when only isolated populations are considered.

The answer in the statement above is true, it is because it is necessary to have large sample because diseases are unpredictable, which will be difficult especially on isolated populations are being considered. Having an isolated population could be hard to the researches because they only have a limited people to observe, that is why they needed a large sample in order to differentiate results and have enough sample to use.

As you stated before, cellulose is found throughout the cell walls of plant cells. Cellulose makes cell walls rigid, so that would indicate that cellulose is a carbohydrate.